Liquid medicaments, such like insulin or heparin or other liquid medicaments such like vaccines that for instance require administering by way of injection, are typically provided and stored in vitreous cartridges, such like carpules, vials or ampoules. With regard to the type of medicament, the material of the cartridge or container has to be inert. Therefore, cartridges made of glass are nowadays typically used for storing and distributing such medicaments.
Glass cartridges comprising a vitreous body of e.g. cylindrical geometry may become subject to fracture if not handled appropriately. In the event of undue care, glass cartridges may break. Even though in industrial filling and packaging processes, glass cartridges or vitreous bodies are generally handled with due care, occasional breakage of particular cartridges may not be entirely prevented. In case a glass cartridge is damaged, respective glass splinters may distribute and the medicament contained in the cartridge may contaminate the environment, in particular neighboring cartridges. In the event, a single glass cartridge is damaged in an industrial manufacturing line, it may become necessary that an entire charge of cartridges has to be visually inspected or discarded at high cost.
In addition, the quality of vitreous barrels or glass cartridges provided form a supplier may be subject to inevitable variations that arise from the glass production or manufacturing process of the respective cartridges.
Macroscopic glass breakage may occur due to a singular or due to repeated impact with a particular force or due to repeated and accumulated enlargement of macroscopic defects, the latter of which are not easily detectable. In typical production or assembly processes, a particular glass cartridge may be exposed to a series of low sized mechanical impacts. Any of these impacts alone does not yet lead to a macroscopic glass breakage. But accumulation of successive impact events may constantly lower the cartridge's integrity. This accumulation of mechanical microcracks or mechanical impact can be denoted as glass memory effect.
Especially with drug delivery devices that are initially equipped with a vitreous cartridge the cartridge has to be assembled in the delivery device during assembly thereof. There, the filled cartridge is inevitably subject to further handling. In a final step of device assembly or during packaging of the device the cartridge may be subject to further mechanical impact which may not damage the cartridge right away but which may harm its integrity on a long term scale. Typically, vitreous cartridges to accommodate a liquid medicament are sealed by e.g. a pierceable septum. In the production and assembly environment not only the vitreous body of the cartridge but also the seal may be subject to almost non-detectable defects that might be uncritical initially. However, such minor damages to the vitreous body, to the seal or to the connection of seal and body may harm the closure integrity of such cartridges on a long term scale.
There exist various methods of testing or determining the glass integrity during or prior to a mass-production, mass-assembly or filling process. Typically, the integrity of a vitreous body can be measured with a selection of tools by applying mechanical stress to the glass body from outside with a well-defined force until the glass body breaks or bursts.
With known non-destructive and non-invasive testing methods, such like optical inspection methods, minor damages, such like micro cracks or similar defects are hardly visible or detectable, e.g. due to low contrast or unfavorable optical inspection conditions. Furthermore, with optical inspection methods the medicament contained in the cartridge is subject to irradiation, which either may harm the medicament or which limits the spectral range of applicable electromagnetic waves. Moreover, some medicaments are light sensitive and have to be stored in colored or dyed cartridges that are generally rather unfavorable and disadvantageous to apply an optical inspection procedure.